We recently uncovered a neural pathway between the hypothalamus and the testes that decreases testosterone (T) independently of pituitary LH, changes in testicular LH receptors or blood flow, and various circulating factors. We showed that the intragastric (ig) injection of alcohol inhibits Leydig cell activity responsiveness to gonadotropins in part through activation of this pathway, and thus independently of peripheral mechanisms. This effect is mimicked by the intracerebroventricular (icv) injection of a small (5 mu l) volume of alcohol that does not cause neuronal damage or leak to the periphery, but quickly and significantly blunts the T response to human chorionic gonadotropin (hCG). Under Specific Aim 1, we will further characterize this pathway by combining the intratesticular injection of the retrograde transganglionic tracer pseudorabies virus with the Fos response that is elicited in various brain regions by the icv injection of alcohol. Specific Aim 2 will focus on the testicular messengers through which alcohol inhibits Leydig cell activity, which has been a long-standing and unresolved issue. Specifically, we will identify some of the molecules whose synthesis is stimulated in the testes by the ig or icv injection alcohol, and that modulate the ensuing loss of Leydig cell activity. We will then turn to hypotheses related to the physiological importance of the proposed neural pathway. Under Specific Aim 3, we will investigate the role of this circuit in mediating the inhibitory influence of alcohol on sexual maturation, then compare this role to that of peripherally-mediated mechanisms such as direct testicular effects exerted by circulating levels of the drug. Finally under Specific Aim 4, we will explore a novel interaction that we recently uncovered between alcohol and other stressors. Specifically, we showed that prior exposure to a modest dose of alcohol, injected icv or ig, increases the ability of mild electrofootshocks to inhibit Leydig cell activity. Here we will test the hypothesis that alcohol exerts this effect by augmenting the effect of stress-related signals on the hypothalamic-testicular pathway. Collectively, these studies will advance our understanding of the effects of alcohol on male reproductive functions and the mechanisms that mediate them.